Preheat oven to 350 degrees Fahrenheit.
In a large bowl, mix together all the dry ingredients (except the nuts and chocolate) with a wire whisk or a fork. Add the liquid ingredients and stir with a wooden spoon or rubber spatula until fully combined. The batter may appear lumpy, as long as all the dry ingredients have been incorporated. Fold in the nuts and chocolate chunks.
Lightly spray the wells of a normal sized muffin tin with cooking spray (preferably canola oil flavor -- which has no flavor), and fill the wells almost full with the brownie batter. There should be between 1/4 and 1/2 inch of room in the well.
Bake the brownie muffins for about 18 minutes, or until the tops are no longer shiny, and a toothpick inserted in the center of a muffin comes out clean.
Allow them to cool about 5 minutes in the pan, and then transfer to a wire cooling rack for at least 20 minutes. Of course, they're completely delectable to eat while they're still warm, but you will want to store them in an airtight container or zippered sandwich bags to keep them moist.